The present invention relates to electric connection members, mounting structures of electronic component assemblies, and intermediate members used for producing electric connection members.
Conventionally, anisotropic conductive films have been used in connection of circuit boards in liquid crystal displays. For such an anisotropic conductive film, the structure is employed in which metal particles are dispersed in an insulating adhesive sheet at a predetermined concentration. An anisotropic conductive film is disposed between two interconnect patterns, for instance, a display circuit board and a drive circuit, and heated and pressurized via a support substrate, whereby metal particles dispersed in the film come into contact with the two interconnect patterns to ensure the conduction.
In the connection between the two interconnect patterns, however, the metal particles and either interconnect pattern are connected on a point basis, and accordingly, when the connected interconnect patterns are bent or when the circuit board or the anisotropic conductive film is expanded and contracted under heating, the metal particles come off from the interconnect patterns, which causes the conduction between the two electrically-connected interconnects to be unstable. Aside from that, such an anisotropic conductive film uses a thermosetting adhesive. Accordingly, when a connection interconnect is bent, cracks may occur in an adhesive layer, and in addition, since the contact area between each interconnect pattern and metal particles is small, upon application of heat and pressure, cracks may occur in interconnect patterns because of metal particles.
Meanwhile, JP 2003-045517 A discloses an electric connection member in which a plurality of elongated lead layers are arranged in parallel to each other and joined and fixed to a joint substrate formed of a thin plate via an adhesive layer, as well as an electrode substrate. The disclosure is described below with reference to, among attached drawings, FIG. 6 corresponding to FIG. 1 of JP 2003-045517 A. In an electric connection member 500 in which a plurality of elongated lead layers 3 are arranged in parallel to each other and joined and fixed to a joint substrate 5 formed of a thin plate via an adhesive layer 4, the lead layers 3 are formed to have a width narrower than that of each strip interconnect 61 of the electrode substrate 600 which is a counterpart in bonding with the electric connection member 500 and in which a plurality of strip interconnects 61 are arranged on a surface of a substrate 6 in parallel to each other and are connection counterparts of the lead layers 3. With this configuration, electric connection can be ensured without damaging opposing interconnect patterns.
In the electric connection member 500 described in JP 2003-045517 A, the lead layers 3 are formed on the adhesive layer 4 having a uniform thickness, and the adhesive layer 4 is formed by applying a pressure sensitive adhesive or an adhesive onto the joint substrate 5 (FIG. 6B). When this electric connection member 500 is connected to the electrode substrate 600 in which the strip interconnects 61 are formed on the surface of the substrate 6 or to an electronic component (e.g., semiconductor device) having an electrode, the adhesive layer 4 can be bonded with both lateral edge portions of a surface of each strip interconnect 61 (FIG. 6B).
In the electric connection member 500 and the electrode substrate 600 of JP 2003-045517 A, however, the lead layers 3 project from a surface of the adhesive layer 4, and the strip interconnects 61 also project from the surface of the substrate 6, so that the surfaces of the adhesive layer 4 and the substrate 6 are not tightly adhered and bonded to each other, resulting in low bonding strength (FIG. 6B).
To cope with it, in the electric connection member 500 and the electrode substrate 600, a metal nano-ink (which refers to an ink that contains metal nanoparticles and can sinter at low temperature) is applied onto the lead layers 3 and sintered between the lead layers 3 and the strip interconnects 61 at low temperature, thereby increasing the bonding strength.
When a metal nano-ink 15 is applied onto surfaces of the lead layers 3 projecting from the adhesive layer 4, however, upon pressing the electric connection member 500 against the electrode substrate 600, the metal nano-ink 15 may flow out between the adhesive layer 4 and the substrate 6 (FIG. 5), and adjacent lead layers 3 may be short-circuited through a conductive thin film formed by sintering. In addition, when an encapsulated metal nano-ink described in JP 2014-184381 A is used as the metal nano-ink, the metal nano-ink may be scattered as capsules are broken, which may lead to a short circuit of adjacent lead layers 3.